Rhodium-catalysed [2 + 2 + 2]-cycloadditions of acetylenes

Abstract

Wilkinson's catalyst [(PPh₃)₃RhCl](0.5–2 mol%) catalyses the chemospecific [2 + 2 + 2]-cycloaddition of hepta-1,6-diynes with monoynes to give polysubstituted benzene derivatives in moderate to good yield. The reaction is favoured by polar solvents such as ethanol and occurs at 0–78 °C. Several examples of intramolecular [2 + 2 + 2]-cycloadditions of triynes are described and a mechanism that accounts for the chemospecificity and observed variations in rates of reaction is discussed.